1. Field
Embodiments of the present invention relate to a method of forming contact holes, and more particularly, to a method of concurrently (or simultaneously) forming contact holes of different depths.
2. Description of Related Art
To increase the degree of integration of wiring in a semiconductor device or a substrate, the semiconductor device or the substrate may include multiple wiring layers. The semiconductor device or the substrate may include a contact hole to couple (or connect) the different wiring layers. The contact hole may include a hole formed in an insulating layer disposed between an upper wiring layer and a lower wiring layer and a conductor disposed within the hole. Thus, the contact hole may electrically couple (or electrically connect) the upper wiring layer and the lower wiring layer.
Holes may be formed in the insulating layer by an etching process. When two or more holes of different depths are formed in the insulating layer, a top surface of the lower wiring layer may be exposed through a relatively shallow hole of the insulating layer. Then, as the etching process continues, polymer created by the reaction of the exposed lower wiring layer with an etching gas may accumulate on sidewalls of the insulating layer inside the hole and sidewalls of photoresist provided on the insulating layer to pattern the hole. The polymer accumulated on the sidewalls of the insulating layer and the photoresist may hinder the etching of the insulating layer in the etching process. Therefore, after the completion of the etching process, residues of the insulating layer may remain on the lower wiring layer whose top surface is exposed through the relatively shallow hole of the insulating layer. The residues of the insulating layer existing on the lower wiring layer may increase the resistance of a contact hole by impeding the upper wiring layer and the lower wiring layer from being coupled (or connected) to each other by the contact hole. In addition, the residues of the insulating layer existing on the lower wiring layer may suppress the adhesion of the upper wiring layer to the lower wiring layer. Therefore, cracks may be created between the upper wiring layer and the lower wiring layer in the contact hole by external impact.